<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style type="text/css">
			#app{
				position: absolute;
				bottom: 0;
				width: 100px;
				height: 100px;
				background-color: red;
			}
			html{
				height: 2000px;
			}
		</style>
	</head>
	<body>
		<div id="app">
			
		</div>
		<script>
			var dfd=new IntersectionObserver((se)=>{
				console.log(se)
			},{threshold:0})
			dfd.observe(document.getElementById("app"))
		</script>
	</body>
</html>